1. Field of the Invention
The invention relates generally to a communication system where a plurality of Core Networks (CNs) shares a common Radio Access Network (RAN). More specifically, the invention relates to a routing procedure in a system of the above-mentioned type. Since the Core Networks are typically operated by different operators, the system is termed a Multi-Operator Core Network (MOCN) in this context. Routing here refers generally to a process during which the RAN, in response to an initial message originated from a user terminal, selects a Core Network for the user terminal.
2. Description of the Related Art
The high price of the licenses for 3rd generation mobile telephone networks (3G) together with the high cost of the 3rd generation network infrastructure deployment requires innovative strategies in the development of the new network infrastructure. For a network operator, an effective way to reduce the investment costs and risks associated with this development is to share the new network infrastructure with other network operators. In many countries the authorities have become favorable for network sharing and allow network operators to form alliances in order to share a part of a network or even the whole network, provided that competition is not hampered.
In the current dynamic market place this development will increasingly result in partnerships and creative agreements between operators. This trend will also emphasize the need for tools that enable the implementation of various degrees of network sharing.
One way of sharing a network infrastructure is a solution where several operators share a common Radio Access Network. In a network like this, a common Radio Access Network is connected to several Core Networks, each being operated by a different operator. This concept is called a Multi-Operator Core Network (MOCN). Despite several operators, the user may, depending on his/her terminal capabilities, see the network as a single network, the identity of which is broadcast by the Radio Access Network.
From the point of view of an operator, the advantages of a MOCN infrastructure are, for example, as follows:
the MOCN allows independent dimensioning of the Core Networks;
the charging entities are located in the Core Network of each operator; and
the MOCN allows complete control of the services provided and also a good control of the quality of service.
In a MOCN network, the Radio Access Network forwards an initial message originating from a user to one of the Core Networks. If the Core Network receiving the initial message from the Radio Access Network cannot serve the user in question, it informs the Radio Access Network accordingly, which then reroutes the initial message to another Core Network to see whether the user can be served by that Core Network.
One problem with the current MOCN networks relates to the rejection of service in a situation in which none of the Core Networks (i.e. operators) are able to provide service to a particular subscriber. In this situation, the last Core Network to which the initial message, which is a NAS (non-access stratum) message, is rerouted, does not know that the message has already been routed to all the other Core Networks of the MOCN and that the other networks are not able to serve the subscriber. Therefore, it is possible that the last Core Network initiates a new rerouting procedure, although no serving Core Network can be found. As there is currently no mechanism for handling these kinds of situations in the Radio Access Network, the Radio Access Network may alternately, upon receiving the service rejection from the last Core Network, release the signaling connection to the user terminal, without properly indicating the reason for the release. Therefore, the user terminal may, after entering the Mobility Management-Idle (MM-IDLE) or Packet Mobility Management-Idle (PMM-IDLE) state, start the whole procedure again.
The above problem typically exists when the subscriber tries to register with the network. The initial message originating from the terminal is therefore also termed a “registration request” in this context.
It is an objective of the invention to bring about a solution whereby it is possible to avoid the above-mentioned drawbacks.